Non-invasive measurement of blood components using retinal imaging

ABSTRACT

Illuminating light of selected wavelengths in the visible or infrared range is projected through the pupil of the eye onto the fundus, and the light reflected back and out through the pupil is detected and analyzed, preferably using the area of the optic disk for analyzing the retinal vessels overlying the optic disk. Specific wavelengths of illuminating light may be chosen for each blood component to be analyzed depending on the spectral characteristics of the substance being analyzed. The reflected image from the retina may be used to measure non-photoreactive blood components such as hemoglobin, and photoreactive components such as bilirubin. For the measurement of photoreactive components, images may be taken before and after, or during, illumination of the eye with light at wavelengths which will affect the photoreactive analyte, enabling measurements of the concentration of the analyte.

This application is a continuation of application Ser. No. 09/534,782,filed Mar. 24, 2000, now U.S. Pat. No. 6,305,804, which claims thebenefit of provisional patent application No. 60/165,195, filed Nov. 12,1999, and of provisional patent application No. 60/126,212, filed Mar.25, 1999.

FIELD OF THE INVENTION

This invention pertains to the field of non-invasive in vivo measurementof blood components such as glucose, hemoglobin, and bilirubin.

BACKGROUND OF THE INVENTION

The measurement of the concentration of blood components such ashemoglobin and glucose has required the drawing of a blood sample for invitro analysis. The need to draw blood for analysis is undesirable forseveral reasons, including discomfort to the patient, the time requiredof medical personnel to draw and handle the samples, and the potentialrisk of spread of disease through punctures of the skin. Repeateddrawing of blood samples is especially undesirable in infants. Manydiabetics must test their blood up to six times a day to monitor theirblood glucose levels. It would thus be desirable to be able to obtainfast and reliable estimates of the concentration of blood components inblood, such as hemoglobin and glucose, through a simple and non-invasivetechnique. Prior efforts have involved an examination of blood in theskin or extremities, such as fingers and ear lobes, or in observablesurface blood vessels, but these efforts have had limited practicalsuccess due to the presence of tissue components that interfere withaccurate reading of only the concentration of blood components.

There are approximately four million newborns in the United States aloneeach year. About 50% of newborns are clinically jaundiced from elevatedbilirubin levels. If the serum bilirubin reaches very high levels duringthe post-natal period, kernicterus, neural damage resulting fromsustained high levels of serum bilirubin, may occur. Frequent monitoringof serum bilirubin is critical to the care of these infants. Of thenewborns that have recognizable jaundice during the first 5 days oflife, 1.7 million receive at least one blood test for bilirubin. Ofthose tested, about 700,000 undergo phototherapy treatment; theseinfants receive an estimated two to three additional blood tests.Presently, blood is drawn through the heel of the neonate, resulting inoccasional infections and other complications. Other drawbacks to thisprocess are its high cost and the delay in lab results reaching thephysician. Recently introduced non-invasive devices for measuringbilirubin do not provide the accuracy level required to diagnose ortreat elevated serum bilirubin levels, rendering them virtually uselessin practice.

SUMMARY OF THE INVENTION

The present invention combines the accuracy of in vitro laboratorytesting of blood components and the advantages of rapidly-repeatablenon-invasive technology. The invention utilizes a hand-held orstationary instrument for retinal imaging that allows non-invasivemeasurement of certain blood components in the retinal blood vessels.Illuminating light of selected wavelengths in the visible or infraredrange is projected into the eye onto the fundus, and the light reflectedback and out (e.g., through the pupil) is detected and analyzed,preferably using the area of the optic disk for analyzing the retinalvessels overlaying the optic disk for most blood components to bemeasured. Specific wavelengths of illuminating light may be chosen foreach blood component to be analyzed depending on the spectralcharacteristics of the particular substance being analyzed. Thereflected image from the retina is utilized to measure blood components,such as hemoglobin, glucose and bilirubin.

The utilization of the retina as a site for obtaining blood componentdata has several advantages, including the ease of visualizing the databecause of the natural window provided by the eye. The reflected lightfrom the fundus at visually significant wavelengths is much lessscattered than light reflected from the skin or mucous membranes sincethe eye is naturally immune to scatter. The retina creates a uniformbackground for imaging, and the optical devices and techniques requiredfor obtaining retinal images have been extensively developed and studiedbecause of the need for ophthalmologists to image the retina fordiagnosis of disease states. In addition, the blood flow to the retinais very even and repeatable even across a number of disease states. Forexample, although patients in shock have reduced blood flow to the skinand mucous membranes, allowing false data to be obtained with currenttechnology that examines the skin and mucous membranes, the bodymaintains even blood flow to the retina except in states of extremelylow blood pressure. Furthermore, in the present invention, there is nophysical contact required between the device and the skin or mucousmembranes, thereby eliminating the potential for transmission ofinfectious agents associated with devices that require patient contact.The device may be rested upon the orbit of the patient for ease of useand, if desired, a disposable plastic cover may be used to furtherminimize the risk of transmission of infectious agents. Such a cover maybe transparent and fully cover the device, or not, depending uponrequirements of the imaging system and the need to prevent incidentalcontact with the device.

In accordance with the invention, a hand-held or stationary instrumentfor retinal imaging may be used to obtain non-invasive measurement ofphotoreactive analytes, an example of which is serum bilirubin.Illuminating light of selected wavelengths in the visible range isprojected into the eye onto the fundus. Specific wavelengths ofilluminating light are chosen so that serum bilirubin can be measured.Analysis of the reflected image from the fundus is utilized to measurebilirubin. Although measurement of the reflected light from the vesselsoverlying the optic disk is preferred, in accordance with the invention,it is also typically possible to obtain bilirubin measurements fromlight reflected from the fundus generally.

During disease states when the serum bilirubin levels are above normal(e.g., newborn jaundice), bilirubin is extruded from the choroid intothe nerve layer of the retina. During newborn jaundice, this nerve layerstains yellow from the elevated bilirubin levels. This yellow color isdirectly proportional to the elevated serum bilirubin levels and changesrapidly with changes in serum bilirubin. The bilirubin molecule exhibitspeak absorption of light at 470 nm. However, when exposed to light at ornear this wavelength, the molecule breaks down into optically inactivemolecules. The intact bilirubin molecule reflects light at and near awavelength of approximately 550 nm (yellow light), and is not affectedby this light. In the present invention, the retina of the patient's eyemay first be imaged with light that does not break down bilirubin, e.g.,light at a wavelength of 550 nm with little or no light at 470 nm. Theintensity of the reflected light at or near the maximum reflectionwavelength of 550 nm is detected. Then the retina is imaged again usinglight that breaks down bilirubin, e.g., using light at 470 nm followedby or combined with light at 550 nm, which is projected into the eye.The reflected light at 550 nm that is passed out through the pupil isdetected to image the retina a second time. With the addition of lightat 470 nm, the bilirubin molecule is rendered optically inactive andwill no longer reflect at 550 nm. The difference in the reflected imageintensity at 550 nm from the first image to the second image is afunction of the bilirubin concentration. A neural network or otherprocessing technique may be used to analyze the two data sets of theimages captured by the retinal camera.

Further objects, features and advantages will be apparent from thefollowing detailed description when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic diagram of an apparatus for measurement of theconcentration of blood components in accordance with the invention.

FIG. 2 is a schematic diagram of a modified form of the apparatus formeasurement of blood components in accordance with the invention.

FIG. 3 is a schematic side view of a hand-held illumination and camerasystem that may be utilized in accordance with the invention.

FIG. 4 is an illustrative front view of the illumination and camerasystem of FIG. 3.

FIG. 5 is a schematic diagram of a further apparatus in accordance withthe invention that incorporates a communications link to a remoteprocessing system.

FIG. 6 is a simplified schematic diagram of apparatus in accordance withthe invention for measuring bilirubin concentration in blood.

FIG. 7 is an illustrative graph of intensity of light at 550 nmreflected from the retina as a function of time, showing the effect ofthe periodic illumination of the eye at 470 nm.

FIG. 8 is an illustrative graph, similar to FIG. 7, of reflected lightintensity over time showing the effect of changes in blood flow in theretinal vessels.

FIG. 9 is a graph of the intensity of light at 550 nm reflected from theretina showing the effect of single pulse illumination at 470 nm.

FIG. 10 is a graph illustrating the correlation between hemoglobinconcentration measured in accordance with the invention versusconcentration measured by a standard in vitro technique.

FIG. 11 are graphs of light absorption as a function of wavelength fordeoxyhemoglobin and oxyhemoglobin.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be used to measure various analytes. Theseanalytes may be photoreactive or non-photoreactive. Table 1 belowsummarizes examples of the preferred methodologies in accordance withthe invention for the measurement of photoreactive and non-photoreactiveanalytes. However, it is understood that these are only illustrative ofthe analytes that may be measured using the present invention.

TABLE 1 Methodologies Target Molecule: Non-Photoreactive AnalytePhotoreactive Analyte Examples: Hemoglobin Glucose BilirubinIllumination: Visible Light IR illumination Discrete wavelength visiblelight IR illumination Target Site: Retinal disk Retinal disk Retinavasculature vasculature Imaging: Single image Multiple images Multipletime lapsed images at different wavelengths Scanned sensor array

Device Description

With reference to the drawings, FIG. 1 illustrates a blood analysisapparatus of the invention in conjunction with the eye of the patient,shown illustratively at 10 in FIG. 1. The blood analysis apparatusincludes an optics system 11 comprised of lenses for projectingilluminating light onto the fundus, generally although not necessarilydirectly through the pupil, and for receiving the light reflected fromthe fundus passed out through the pupil, and for focusing that light toform an image. The lenses preferably include a final lens which can bepositioned close to (e.g., approximately 3 mm from) the cornea of theeye, providing a 10 to 30 degree conical view of the retina to beilluminated and imaged. Such lens systems are of conventional design andare utilized for macroview lens systems in retinal video cameras.

An illumination system 12 provides selected illuminating light forviewing and imaging the retina. The illumination system is preferably amonochromatic or multiple discrete wavelength light source that provideslight for viewing and imaging the retina. Preferably, the systemprovides light for viewing and imaging coaxially to reduce thelikelihood of extraneous reflections from the interior or exterior ofthe eye. The light from the illumination system may be projected throughthe pupil. The frequency content of this light source is selecteddependent upon the compound to be analyzed. Illumination light may becomposed of two (or more) separate lighting systems, such as a xenonstrobe, or multiple laser diodes, for imaging, and a halogen source forviewing. Infrared imaging may be done utilizing a filtered halogen orlaser diode source. The light is reflected from the fundus of the eye 10and passed through the pupil opening of the eye to the optics system 11and through the illumination system 12, entering, e.g., a charge coupleddevice (CCD) detector 22. The illumination system 12 may be similar tosystems used in existing non-mydriatic fundus cameras, preferablymodified to provide a coaxial design for illumination and imaging. Aviewing system 14, for example, a liquid crystal display (LCD) screen,may receive the image data and display the image for use by the operatorfor initially locating the patient's retina, based on an image from theoptical system in real time. A coaxial “scene” or visual target may beincluded in the visual field of the device so that a patient can fixatehis or her eye on this scene and reduce eye motion. In addition toreducing eye motion, the location of this visual target will bring theoptic disk into the approximate center of the CCD detector. In devicesintended for children, the scene may include a visually pleasant objectsuch as a familiar animal. In the currently commercially available videocameras designed for retinal imaging, the LCD (or other display) screenis typically located on a desktop power source that is attached to thehand-held camera by a cable. While such displays may be used in thepresent invention, the LCD screen (or other display device) ispreferably placed on the back of the hand-held camera unit, so that theoperator can more easily locate the retina, having the patient's eye andthe LCD screen in the same line-of-sight. Current retinal video camerasystems that may be modified and utilized in the invention and whichinclude an optics system 11 and an illumination system include the NidekNM100 Hand-Held Non-Mydriatic Fundus Camera and the Topcon TRC-50EX(TRC-NW5S/TRC-NW5SF) Non-Mydriatic Retinal Camera. The Nidek NM100camera utilizes a coaxial imaging system with an infrared source, withimaging done through reflected light outside the optical system.Although the invention may be carried out with a dilated eye pupil, itis preferable that the imaging of the retina be carried out withoutrequiring dilation of the pupil for speed of measurement and patientconvenience. The camera preferably includes a shield (not shown) toprevent ambient light from entering the optical system 11 to minimizeextraneous reflections and the introduction of optical noise.

The optical system 11 also interfaces with a locate and focus system 16,which utilizes feedback from an image capture system 17, also interfacedto the optic system 11, to automatically find and bring the optic diskinto focus. A convolver or other pattern recognition software may beutilized to locate the optic disk area by finding the circular patternof the optic nerve area. After using the pattern recognition informationto more precisely locate the optic nerve area in the center of theviewing field, the image may then be magnified using a series of lensesin the optics system 11 such that the optic disk area virtually fillsthe active area of the CCD (or other detector). The optical systempreferably tracks the movement of the fundus while zooming the opticssuch that the optic disk is centered and occupies most of the opticalfield of view. The optical system may be formed to track the motion ofthe fundus through a motor drive system that slightly gimbals the lenssystem. This motion system is driven and controlled in a closed loopmanner utilizing the feedback of the pattern recognition software.

The image capture system 17 is selectively controlled by the operatorand uses feature and pattern recognition to drive the locate and autofocus system 16 to capture and store an appropriate image for analysis.Image capture itself is analogous to the function provided by a “digitalstill camera.” The image capture system may utilize feature and patternrecognition to drive the locate and focus system to capture and store anappropriate image for analysis. Commercially available patternrecognition software may be used. Actual imaging is preferably timedbased on the patient's blood flow, which is preferably sensed from bloodvessels through the patient's skin around the ocular structure through asystolic sensing system 13. The light reflected from the retina ispreferably detected and an image formed at the time of systole, thusensuring the maximum blood flow in the vasculature of the retina.Detection of the patient's systolic state can be made through anycommonly known means such as commercially available blood pressuretransducers. An image analysis system 18 is interfaced with the imagecapture system 17 to analyze the light reflected from the retina toquantitatively determine the amount of the particular target analytecompound present. The results may be displayed to the operator via theoutput system 20. This system presents results as well as any feedbackassociated with the acquisition of the data, and may include an LCDdisplay screen or other display devices.

A modified imaging methodology as shown in FIG. 2 may also be usedwherein an imaging device 21 functions in a scanning mode (which may besimilar to that utilized in common video cameras) to provide multipleimages of the retina to the image capture system 17. The imagerecognition system 15 then acts to select a valid image from the seriesof images stored by the image capture system 17. Once selection of anappropriate image is made, calculation of the magnitude of the desiredanalyte proceeds using the image analysis system 18 as before. Imagevalidity is based on focus, closeness to center of the fundus, andobliqueness of the fundus in the image.

FIG. 3 illustrates a hand-held camera and illumination unit 25 for theanalysis system of the invention in which the optic system 11 ismounted, and FIG. 4 illustrates the output viewing system 14 at the backend of the hand-held unit 25 to enable the operator to review the imagebeing obtained of the retina on a real-time basis. If desired, adisposable transparent plastic (e.g. polyethylene, polystyrene,polypropylene, etc.), which is selected to transmit light in thewavelengths required, may be used to cover the unit 25 during use andthen disposed of to minimize the risk of transmission of infection. Eyeinfections are particularly common in newborns and a cover would assistin the prevention of these infections. Furthermore, the cover mayinclude a soft portion (e.g. foam) that comes into contact with the skinaround the orbit. This makes the cover comfortable and, in addition,prevents ambient light from entering into the camera lens duringmeasurements.

Currently available CCD detectors may not be sensitive to wavelengthslonger than approximately 1000 nm. In measuring analytes requiring thesensing of these longer wavelengths, an alternative approach may beused. The illumination source may instead scan across the area ofinterest on the retina, with the reflected beam being read by a singlesensor (or a small multiplicity of sensors) that are sensitive in theinfrared (IR) wavelengths above normal CCD sensitivity. This method maybe used to digitally reconstruct the retinal image if desired.

As illustrated in FIG. 5, image processing and analysis may take placeat a location remote from the clinical setting by using a wired orwireless internet link (or dedicated communication link) to transferdata from the image capture system 17 to a central computer at a remotelocation (i.e., anywhere in the world linked by the internet) at whichthe image analysis system 18 is implemented. The output data from theoutput system 20 may be transferred back through an access link 29 tothe viewing system 14 at the clinic (or to another location, asdesired).

Non-Photoreactive Analyte (Hemoglobin) Measurement

In one implementation of the device for the detection of hemoglobinusing multiple beam splitters, the image of the optic disk returningfrom the eye may be split into three simultaneous and equal images. Eachimage is then passed through a filter with the preferred wavelengths forthe images of 640, 766 and 800 nm. Different wavelengths of light areused for the analysis of other substances such as glucose. Althoughthese preferred wavelengths will yield accurate measurement ofhemoglobin, other wavelengths in the visible or near IR may also be usedeffectively by this invention for hemoglobin.

To obtain accurate measurements of hemoglobin concentration withouthaving to account for different levels of oxygen saturation, themeasurement of hemoglobin may be carried out in the present inventionusing wavelengths of light at which the extinction coefficients foroxyhemoglobin and deoxyhemoglobin match. Thus, the total absorption ofenergy at that wavelength will be proportional to the total hemoglobin.Examples of such wavelengths are 550 nm and 800 nm. Absorption curvesfor oxyhemoglobin (HbO₂) and deoxyhemoglobin (Hb) as a function ofillumination wavelength are shown in FIG. 11. As illustrated therein,the absorption curves are closely matched in the wavelength range fromabout 380 nm to 580 nm, and particularly from about 530 nm to 580 nm,allowing most (or all) wavelengths in these ranges to be used.

The areas that are preferably used for analysis are the retinal arteriesand veins overlaying the optic disk. Previous work by Hickam et al.suggested that when the optic disk is illuminated with light directedtoward the fundus, the optic disk acts as a light source directing thelight back through the retinal vessels that lay over the disk. See, JohnB. Hickam, et al., “A Study of Retinal Venous Blood Oxygen Saturation inHuman Subjects by Photographic Means,” Circulation, Vol. XXVII, March,1963, pp. 375-385. Hickam, et al. believed that these vessels thenfunctioned as cuvettes, filled with blood, that could be analyzed by thespectral pattern that is measured from the light passing through thesevessels and emitted out through the pupil. In actuality, light does notpass through these vessels and reflect off the optic disk and then passthrough these vessels again as suggested in Hickam, et al. Instead,light reflects directly off the surfaces of these vessels and the bloodcomponents within these vessels. In the present invention, the retinalarteries are the sub-target areas that are analyzed by measuring theamplitude of the signal at each selected wavelength. This is done bydetermining the effective reflected image intensity of the pixels forthe sub-target areas corresponding to the arteries at each selectedwavelength. Within the sub-target area, the peak concentration of bloodis determined by viewing the peak absorption at each measuredwavelength. The sub-target area is then normalized by this peak and thenmay be averaged using any common digital averaging technique, such as aconvolver. Within the sub-target area, a histogram is created torepresent different signal levels after averaging. These data comprisedof histogram values and values representing the rate of change in localintensity are then the direct input into an analysis program, e.g., aneural network, for analysis. A computer implemented neural network ispreferably utilized to analyze the pixel data for comparison to knownblood concentrations. A preferred type of neural network is BackPropagation.

The effect of differences in illumination from one retinal image toanother is preferably neutralized by comparing the backgroundillumination of the optic disk to the vessel illumination and “zeroing”for differences in illumination. This allows the input from thesub-target areas to be consistent from patient to patient and camera tocamera.

Although the present invention is well suited to be carried out on a“real time” basis with the apparatus of FIGS. 1 and 2 as describedabove, it may be implemented using photographic fundus images which arescanned and processed. As an example of the present invention usingphotographic images, a group of individuals was tested to measurehemoglobin levels utilizing the present invention. A standard in vitrotest was also performed on a sample of blood drawn from each individual.The clinical data were obtained as follows. Each ophthalmologist in theclinic agreed to refer for study patients that already had their eyesdilated. A physician asked the patient if they would agree to have theireyes photographed and to allow blood to be obtained for a hemoglobintest. An informed consent document was signed by each patient. A retinalphotographer with the clinic took all of the retinal photographs. Theslide film used was Kodachrome 64 Select, 24 exposures per roll. Thephotographer took photos of each eye, with the fovea centered in thepicture. The exact same conditions were used for each photographincluding aperture, shutter speed, and illumination. A code was givenfor each patient to insure confidentiality and to allow accuratetracking of each patient. The code appeared on each photograph and thesame code appeared on the blood tube.

A licensed phlebotomist obtained antecubital blood samples from eachpatient. These samples were drawn with vacutainers into purple-top tubesfor later analysis. The tubes were stored cold and run the same evening.Following the analysis, the blood tubes were saved if later analysiswere required. The blood samples were analyzed for hemoglobin contentwith a HemoCue® B-Hemoglobin Analyzer. The machine was calibrated withcalibration slides. This device is CLIA certified and the technician whoanalyzed the samples was also CLIA certified. Each sample was run threetimes on the machine to ensure accurate results. These results wererecorded along with the patient's ID code. Kodachrome 64 Select SlideFilm was used for each retinal photograph. The film was sent to Kodakfor processing. The Kodak development lab used the same lot of chemicalsfor all of the slides. The developed slides were then scanned into adigital format (jpeg files) with a Polaroid Sprintscan 4000 scanner.

Multiple images of each subject were taken, and images were selected foranalysis based on uniformity of illumination, quality of focus,obliqueness of fovea to illumination axis, and systole status. The(normalized) green portion of the RGB image data in the jpeg file wasused for analysis, where green =G/(R+G+B). As illustrated in FIG. 11, inthe green wavelength range (about 500 nm to 550 nm), the absorption ofoxy- and deoxyhemoglobin is similar. The image analysis proceeded withthe following steps for each selected image:

Find the optic disk.

Create a circular area of data entirely within the optic disk that isless in diameter than the optic disk. Convolve the data in this circlewith a small convolver (0.5 mm) to smooth the data.

Find the maximum and minimum levels of green in pixels within thecircle. Use this min. level to normalize the values of all pixels withinthe circle.

Compute the gradient of green within the circle.

Find the centroid of the gradient magnitude.

Construct a circle (subtarget) of the image that is approximately 0.5 mmin diameter centered at the centroid and within the disk. (Thisprocedure locates a sub-target area within a retinal vessel in the opticdisk.)

Using the data in the pixels having green magnitudes in the range of25-45% of the maximum level of green in the subtarget, create ahistogram of this area with 5 buckets for values and 5 buckets forderivative magnitudes. For each magnitude range, calculate the averagederivative (gradient) magnitude and average magnitude.

These values then become the input for a learning algorithm, such as aneural network simulation, which is trained to associate measuredhemoglobin with the data sets.

The neural net employed for exemplification was the “Back Propagation”neural net which is contained in the MATLAB Toolbox of MATLAB Version5.3.

The neural net is trained with the data sets determined above by thefollowing technique:

(a) remove one data set (representing one image) from the total numberof sets.

(b) use the data sets remaining to train the neural net mentioned above.

(c) use the trained neural net to calculate a hemoglobin value from thedata set left out at step (a) above.

By repeating the neural net calculation above, a curve was constructedof non-invasively calculated values versus actual lab values.

Correlation data showing the measurements of hemoglobin concentrationfor each individual as determined in accordance with the presentinvention versus the hemoglobin measurement values obtained by the invitro laboratory measurements are shown in FIG. 10. These data indicatea strong correlation, 0.89, between the measurements obtained by thepresent invention and measurements obtained by standard in vitrolaboratory techniques.

The results of the analysis of the serum concentration values of theblood components may be displayed on an output system 20 to theoperator. The output system 20 may utilize the LCD screen 14 of theviewing system to present data to the operator as well as feedback onany problems occurring with the acquisition of the image or the device.In the event that the image is not acceptable and will not allow thedevice to calculate accurate blood values, the output system 20preferably prompts the operator to capture another image.

In a subset of the patient population, because of particular anatomicalcharacteristics of the eye, various degrees of light scattering may beencountered. This scattering of the light may be the result of variousdisease states including senile cataracts. A polarized light source maybe included in the device to measure the degree of scattering. Thereturned light at orthogonal polarization may be used as a measure ofscattering. This data is fed into the neural network as the scatteringvariable from patient to patient to allow the device to account for thisvariable.

Several analytes that are measured with the device of the invention arealso secreted into the anterior chamber of the eye. The aforementionedembodiment of the device directs light through the anterior chamber tothe retina. The image returned from the retina again passes through thisarea of the eye. The presence of the analyte in this section of the eyecould create false data sets and render the device inaccurate.Therefore, when measuring analytes such as glucose that are present inthe anterior chamber, the light may be directed along an alternate pathto the retina. The illuminating light emitting from the device may bedirected toward the retina at an angle into the eye just lateral to thecornea near the corneoscleral junction (limbus). This angle avoids lightpassing through the anterior chamber of the eye. The exiting light wouldthen be detected at an angle at the opposite side of the eye, again justlateral to the cornea near the corneoscleral junction (limbus). Althoughthis area near the surface of the eye is not optically clear in thevisual range of the electromagnetic spectrum, it is transparent in thelonger wavelengths (>1000 nm) needed to measure analytes such asglucose.

Photoreactive Analyte (Bilirubin) Measurement

Further in accordance with the present invention, the concentration of aphotoreactive analyte may be determined by taking advantage of itsphotoreactivity. For example, bilirubin concentration may be determinedby taking advantage of the fact that the bilirubin molecule exhibitspeak absorption of light at 470 nm, and that at or near this wavelengththe molecule breaks down into optically inactive molecules. Thebilirubin molecule will also effectively break down when exposed tolight in the range of 470 nm±30 nm. The bilirubin molecule ordinarilyreflects light maximally at or near a wavelength of approximately 550 nm(yellow light). In accordance with the invention, a time lapse image ofthe retina may be made wherein the first image is illuminated at 550 nm(±30 nm) followed by a second image illuminated at 470 nm (±30 nm) and athird image illuminated at 550 nm (±30 nm). The second and third imagesare separated in time sufficiently that the photoreactive analyte willchange chemical state. In the case of bilirubin, the change is a almostinstantaneous and the two wavelengths may be projected simultaneously aswell as sequentially. The first exposure provides an image including thephotoreactive analyte (bilirubin in this example) while the thirdexposure provides a reference point for this patient without thephotoreactive analyte (bilirubin in this example) present. Theconcentration of the photoreactive analyte can be computed using aneural net or other well known analysis process based on differences inthe first and third exposures. Light at wavelengths other than 550 nmmay also be used to illuminate the retina as long as such wavelengths donot precipitate a photo-chemical reaction from the analyte (bilirubin inthis example).

In one embodiment of the invention, with reference to FIG. 6 and withbilirubin as the target analyte, light at a wavelength of 550 nm isdirected on a beam 30 to a partially transmissive and reflective mirror31, passing therethrough on a beam path 32 to a beam splitter 34 andthence to the eye 10. The light at a wavelength of 550 nm is directed atthe retina to create a first image. Light from a source at 470 nm isprovided on a path 36 to the partial mirror 31 and is reflected on thepath 32 through the beam splitter 34 to the eye 10. The reflected lightat 470 nm is directed by the element 34 on a path 37 to an absorber 38.The light at 470 nm is pulsed onto the retina at very short timeintervals. With each pulsation of light at 470 nm, the bilirubinmolecule is rendered optically inactive and is not reflected from theretina at 550 nm. As illustrated in FIG. 7, the reflected 550 nm lightintensity is high at the intervals 40 when there is no 470 nm lightillumination and is lower at the intervals 41 at which the 470 nm lightis applied. The difference in reflected light intensity from the peak tothe trough with each pulsation is a function of the bilirubinconcentration. The time intervals 40 and 41 chosen will be dependent onthe blood flow to the retina. FIG. 8 illustrates the change over timewith blood flow. A time interval is required such that there is apartial filling up of the retinal circulation by blood that containsbilirubin. The invention may also be implemented using a single pulseapplication of 470 nm light to measure the bilirubin concentration asshown in FIG. 9.

The data corresponding to the returned light at 550 nm comprised ofpixel values are then the direct input into a neural network or otherwell known procedure for analysis. A neural network is preferablyutilized to analyze the pixel data for comparison to known bloodconcentrations of bilirubin. The difference in pixel data from reflectedlight at 550 nm before and after the 470 nm light pulse is a directfunction of the serum bilirubin level.

The results of the serum values of the bilirubin may be displayed on anoutput system 20 to the operator. The output system 20 may utilize theLCD screen of the viewing system to present data to the operator as wellas feedback on any problems occurring with the acquisition of the imageor the device. In the event that the image is not acceptable and willnot allow the device to calculate accurate bilirubin values, the outputsystem 20 preferably prompts the operator to capture another image.Other photo-reactive analytes may be measured in a manner analogous tothe measurement of bilirubin as discussed above.

It is understood that the invention is not limited to the embodimentsset forth herein as illustrative, but embraces all such forms thereof ascome within the scope of the following claims.

What is claimed is:
 1. Apparatus for detection of the concentration of ablood component in an individual comprising: (a) means for projectinglight having selected wavelengths into an eye of an individual toilluminate the fundus; (b) means for detecting the light reflected fromthe fundus and for forming an image of a portion of the funduscontaining blood vessels; and (c) means for analyzing selectedwavelength components in the detected light from the blood vessels inthe image to determine the concentration of a selected blood component.2. The apparatus of claim 1 wherein the selected blood component ishemoglobin.
 3. The apparatus of claim 1 wherein the selected bloodcomponent is glucose.
 4. The apparatus of claim 1 wherein the selectedblood component is bilirubin.
 5. The apparatus of claim 1 wherein themeans for analyzing selected wavelength components analyzes only lightfrom the regions of the image corresponding to blood vessels.
 6. Theapparatus of claim 1 wherein the light projected into the eye by themeans for projecting contains wavelengths in the visible or nearinfrared range and wherein the means for detecting the light reflectedfrom the fundus includes means for detecting the light in the visible ornear infrared range.
 7. The apparatus of claim 1 wherein the means forforming an image forms an image of the blood vessels in the regionoverlying the optic disk of the eye and wherein the means for analyzingthe wavelength components analyzes the light reflected from the opticdisk.
 8. The apparatus of claim 1 including means for sensing the bloodflow of the individual being tested to detect systole and for using thisinformation to time the detecting of the light reflected from the fundusand forming of an image.
 9. The apparatus of claim 1 wherein the meansfor detecting the light and forming an image forms multiple images ofthe fundus at discrete times over a period of time and selects an imagefrom the multiple images and analyzes that image to determine theconcentration of the blood component.
 10. The apparatus of claim 1wherein the means for detecting the light and forming an image splitsthe detected light into multiple images that are passed through filtersthat pass different wavelengths to provide multiple filtered images, andthe means for analyzing analyzes the multiple filtered images todetermine the concentration of the blood component.
 11. The apparatus ofclaim 10 wherein the blood component is hemoglobin and the multipleimages are filtered to pass light centered at wavelengths of 640 nm, 766nm and 800 nm.
 12. The apparatus of claim 1 including means fortransmitting data corresponding to the image over a communications linkto a remote location, and wherein the means for analyzing selectedwavelength components is located at the remote location.
 13. Theapparatus of claim 1 wherein the means for projecting light into the eyeprojects light through the pupil of the eye onto the fundus.
 14. Theapparatus of claim 1 wherein the means for projecting light into the eyeprojects light on a path at an angle into the eye just lateral to thecornea, near the corneoscleral junction.
 15. Apparatus for detecting theconcentration of a photoreactive analyte in the blood of an individualcomprising: (a) means for projecting light into the eye of an individualto illuminate the fundus that contains wavelengths not including lightat wavelengths that will break down the photoreactive analyte and fordetecting the light reflected from the fundus to determine the intensityof the reflected light at these wavelengths; (b) means for projectinglight into the eye to illuminate the fundus containing wavelengths thatbreak down the photoreactive analyte and for projecting light into theeye to illuminate the fundus containing the wavelengths that do notbreak down the photoreactive analyte, and for detecting the intensity ofsuch light reflected from the fundus; and (c) means for determining thedifference between the intensity of light detected with no wavelengthsthat break down the photoreactive analyte projected on the fundus andthe intensity of light detected when light which breaks down thephotoreactive analyte has been projected onto the fundus, from which theanalyte concentration may be determined.
 16. The apparatus of claim 15wherein the target analyte is bilirubin or an associated molecule. 17.The apparatus of claim 16 wherein the means for projecting light thatdoes not break down bilirubin projects light that does not containwavelengths in the range of 470 nm±30 nm.
 18. The apparatus of claim 17wherein the light projected that does not break down bilirubin containslight centered at 550 nm.
 19. The apparatus of claim 17 wherein themeans for projecting light that breaks down bilirubin projects lighthaving wavelengths in the range of 470 nm±30 nm.
 20. The apparatus ofclaim 16 wherein the means for projecting light into the eye containingwavelengths that break down the photoreactive analyte and for projectinglight containing the wavelengths that do not break down thephotoreactive analyte projects light containing wavelengths centered at470 nm and at 550 nm simultaneously.
 21. The apparatus of claim 16wherein the means for projecting light into the eye containingwavelengths that break down the photoreactive analyte and for projectinglight containing the wavelengths that do not break down thephotoreactive analyte projects light centered at 470 nm followedthereafter by projecting light containing wavelengths centered at 550 nmto illuminate the fundus, and wherein the light centered at 550 nmreflected from the fundus is detected.
 22. A method of detecting theconcentration of a photoreactive analyte in the blood of an individualcomprising: (a) projecting light into the eye of the individual toilluminate the fundus that contains wavelengths not including light atwavelengths that will break down the photoreactive analyte and detectingthe light reflected from the fundus and for forming an image of aportion of the fundus containing blood vessels and determining theintensity of the reflected light at these wavelengths in the image; (b)projecting light into the eye to illuminate the fundus containingwavelengths that break down the photoreactive analyte, and projectinglight into the eye to illuminate the fundus containing the wavelengthsthat do not break down the photoreactive analyte and detecting the lightreflected from the fundus and forming an image of a portion of thefundus containing blood vessels and determining the intensity of thereflected light in the image at the wavelengths that do not break downthe photoreactive analyte; and (c) determining the difference betweenthe intensity of light detected with no wavelengths that break down thephotoreactive analyte projected on the fundus and the intensity of lightdetected when light which breaks down the photoreactive analyte has beenprojected onto the fundus, from which the analyte concentration may bedetermined.
 23. The method of claim 22 wherein the target analyte isbilirubin or an associated molecule.
 24. The method of claim 23 whereinin the steps of projecting light that do not break down bilirubin, thelight projected does not contain wavelengths in the range of 470 nm±30nm.
 25. The method of claim 24 wherein the light projected that does notbreak down bilirubin contains light centered at 550 nm.
 26. The methodof claim 24 wherein the step of projecting light that breaks downbilirubin comprises projecting light having wavelengths in the range of470 nm±30 nm.
 27. The method of claim 23 wherein step (b) includesprojecting light containing wavelengths centered at 470 nm and at 550 nmsimultaneously.
 28. The method of claim 23 wherein step (b) is carriedout by projecting light centered at 470 nm followed thereafter byprojecting light containing wavelengths centered at 550 nm to illuminatethe fundus, and wherein the light centered at 550 nm reflected from thefundus is detected.
 29. The method of claim 22 wherein in the steps ofdetermining the intensity of the reflected light in the image, theintensity of reflected light is determined only from the regions of theimage corresponding to blood vessels.
 30. Apparatus for detecting theconcentration of a photoreactive analyte in the blood of an individualcomprising: (a) means for projecting light into the eye of an individualto illuminate the fundus that contains wavelengths not including lightat wavelengths that will break down the photoreactive analyte and meansfor detecting the light reflected from the fundus and for forming animage of a portion of the fundus containing blood vessels anddetermining the intensity of the reflected light at these wavelengths inthe image at the wavelengths that do not break down the photoreactiveanalyte; (b) means for projecting light into the eye to illuminate thefundus containing wavelengths that break down the photoreactive analyteand for projecting light into the eye to illuminate the funduscontaining the wavelengths that do not break down the photoreactiveanalyte, and means for detecting the light reflected from the fundus andfor forming an image of a portion of the fundus containing blood vesselsand for determining the intensity of the light reflected from thefundus; and (c) means for determining the difference between theintensity of light detected with no wavelengths that break down thephotoreactive analyte projected on the fundus and the intensity of lightdetected when light which breaks down the photoreactive analyte has beenprojected onto the fundus, from which the analyte concentration may bedetermined.
 31. The apparatus of claim 30 wherein the target analyte isbilirubin or an associated molecule.
 32. The apparatus of claim 31wherein the means for projecting light that does not break downbilirubin projects light that does not contain wavelengths in the rangeof 470 nm±30 nm.
 33. The apparatus of claim 32 wherein the lightprojected that does not break down bilirubin contains light centered at550 nm.
 34. The apparatus of claim 31 wherein the means for projectinglight that breaks down bilirubin projects light having wavelengths inthe range of 470 nm±30 nm.
 35. The apparatus of claim 31 wherein themeans for projecting light into the eye containing wavelengths thatbreak down the photoreactive analyte and for projecting light containingthe wavelengths that do not break down the photoreactive analyteprojects light containing wavelengths centered at 470 nm and at 550 nmsimultaneously.
 36. The apparatus of claim 31 wherein the means forprojecting light into the eye containing wavelengths that break down thephotoreactive analyte and for projecting light containing thewavelengths that do not break down the photoreactive analyte projectslight centered at 470 nm followed thereafter by projecting lightcontaining wavelengths centered at 550 nm to illuminate the fundus, andwherein the light centered at 550 nm reflected from the fundus isdetected and the intensity of such light is determined.
 37. Theapparatus of claim 31 wherein in the means for determining the intensityof the reflected light in the image, the intensity of reflected light inthe image is determined only from the regions of the image correspondingto blood vessels.